I have bought a PIR (9695V) for our upstairs landing lights. The circuit is as follows: Three switches: a switch downstairs, another switch upstairs as well as a dimmer switch upstairs. Two led lights upstairs on the landing. Does the PIR need to be wired in between the last switch and the first light or can it go between the two lights in the circuit? I am not sure which of the two upstairs switches is the last switch and without lifting a lot of boards in the loft I'm not sure how I can tell. I have fitted a PIR before but this was in the garage so installation was a lot simpler. Any advice would be greatly appreciated.